ES2939694T3 - Positive electrode material, its preparation method, and lithium ion battery - Google Patents

Abstract

A positive electrode material, a preparation method therefor, and a lithium ion battery are provided. The positive electrode material comprises positive electrode material particles, the positive electrode material particles comprising a central region, an intermediate layer and a surface layer; the intermediate layer is located between the central region and the surface layer; the central region contains lithium oxide, the middle layer contains elemental sulfur, and the surface layer contains elemental sulfur and elemental carbon; lithium oxide comprises δLiNimConX(1-mn)O2·(1-δ)Li2MO3, where 0<=δ<=1; X comprises at least one selected from Mn, Al, Nb and Fe; M comprises at least one selected from Mn, Al, Nb, Fe, Co and Ni; 0<=m<1 and 0<=n<1. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Positive electrode material, its preparation method, and lithium ion battery

Field

This application is related to the field of materials and new energies and, in particular, to a cathode material, its preparation method and a lithium ion battery.

Background

Among various types of new energy batteries, due to high specific energy, high voltage, low self-discharge, good safety performance and long service life, the lithium ion battery has attracted great attention and has been successfully industrialized. The main components of the lithium ion battery include an electrolyte, a separator material, and a cathodic and anodic material. The cathode material of the lithium ion battery occupies a large proportion in the battery, and the performance of the cathode material directly affects the performance of the battery, so the cathode material is the key to the development and improvement of the performance of the lithium ion battery.

Summary

In the prior art, elemental sulfur is added to the cathodic material

of the cathode material, thus increasing the theoretical specific capacity of the battery. In addition, CN 108 183206 A describes cathodic active materials based on mixed lithium metal oxides coated with silicon oxide and aluminum oxide.

In one aspect of this application, this application provides a cathode material. The cathode material comprises cathode material particles, wherein the cathode material particles include a core area, an intermediate layer, and a surface layer, wherein the intermediate layer is located between the core area and the surface layer; and the central area comprises lithium oxide, the middle layer comprises elemental sulfur, and the surface layer comprises elemental sulfur and elemental carbon, wherein the lithium oxide comprises 5LiNi ^m Co ⁿ X ^(1-mn) O ² -( 1-5)Li ² MÜ ³ , where 0 < 5 < 1, X includes at least one selected from Mn, Al, Nb, and Fe, M includes at least one selected from Mn, Al, Nb, Fe, Co, and Ni , 0 < m < 1, and 0 < n < 1. The cathode material particle precursor of the cathode material has pores suitable for filling elemental sulfur, and the pores can protect elemental sulfur from being dissolved in the electrolyte . Elemental carbon can further prevent elemental sulfur from dissolving in the electrolyte and is beneficial in improving the overall electrical conductivity of the material. The particulate structure of the cathode material does not reduce the overall packing density of the cathode material and is beneficial in increasing the volumetric energy density of the cathode material.

In another aspect of this application, this application provides a method of preparing a cathode material comprising particles of cathode material. The method comprises: mixing a solution containing metal ions, a complexing agent and a precipitating agent with stirring, co-precipitating to obtain a nucleo precursor, and mixing the nucleo precursor with a lithium source and firing to obtain a material particle precursor. formed by the packing of lithium oxide and comprising a precursor core area and a precursor surface layer located outside the precursor core area, wherein the metal includes at least one of Mn, Al, Nb, and Fe, and the lithium oxide comprises 5LiNi ^m Co ⁿ X ^(1-mn) Ü ² -(1 -5)Li ² MÜ ³ , 0 < 5 < 1, X includes at least one selected from Mn, Al, Nb, Fe, Co, and Ni, M includes at least one selected from Mn, Al, Nb, Fe, Co, and Ni, 0 < m < 1, and 0 < n <1; mixing the cathode material particle precursor with a sulfur source, melting and solidifying, to fill the surface layer with the elemental sulfur and obtain a sulfur-containing cathode material particle precursor; mixing the sulfur-containing cathode material particle precursor with a carbon source and forming elemental carbon on the outer surface of the sulfur-containing cathode material particle precursor; and dispersing the elemental sulfur by thermal melting and interpenetration treatment, to obtain cathodic material particles with a surface layer comprising elemental sulfur and elemental carbon. The cathode material particle precursor obtained in the above method has a microstructure suitable for elemental sulfur filling, thus preventing elemental sulfur from dissolving in the electrolyte. Elemental carbon can further prevent elemental sulfur from dissolving in the electrolyte and is beneficial in improving the overall electrical conductivity of the material. The particulate structure of the cathode material does not reduce the overall packing density of the cathode material and is beneficial in increasing the volumetric energy density of the cathode material.

In another aspect of this application, this application provides a lithium ion battery. The lithium ion battery includes the above cathode material or the cathode material prepared by the above method. Therefore, the lithium ion battery has a higher energy density and a better cycle life.

Brief description of the drawings

Fig. 1 is a process flowchart of a preparation method according to an embodiment of the present application.

Fig. 2 is a process flowchart of a preparation method according to an embodiment of the present application.

Fig. 3 shows a scanning electron microscopy (SEM) image of a cathode material particle precursor prepared in one embodiment of the present application.

Fig. 4 shows an SEM image of a sulfur-containing cathode material particle precursor formed with elemental carbon prepared in one embodiment of the present application.

Fig. 5 shows an SEM image of cathode material particles prepared in one embodiment of the present application.

Detailed description

Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, where the same or similar items or items having the same or similar functions are indicated by the same or similar reference numerals. throughout the description. The embodiments described below with reference to the attached drawings are exemplary and used only to explain the present application, and should not be construed as a limitation of the present application.

The extremes of all ranges and all values described herein are not limited to precise ranges or values, and these ranges or values are to be understood as including values close to these ranges or values. For intervals of values, the extreme values of the intervals, the extreme values of the intervals and the split point values, and the split point values can be combined together to obtain one or more new value intervals. These ranges of values are to be interpreted as specifically described herein.

The present authors find through long-term experiments that due to the electronic inertness of sulfur and the easy dissolution in an organic solvent of a sulfur intermediate during lithium intercalation, the sulfide ion-containing cathode material suffers further limitation. in practical applications. Although the above problem can be alleviated to some extent by adding carbon as a carrier to the cathode material, simply relying on elemental carbon to segregate the electrolyte and prevent sulfur from dissolving in the electrolyte will not only increase the production cost of the cathode material, it will extend the production process and reduce the production efficiency, but also make it difficult to fundamentally solve the above-mentioned problem of sulfur-based cathode materials. After in-depth investigation, the present authors find that in sulfur-based cathode materials, the problem of easy dissolution of sulfur in the electrolyte is largely caused by the structure of the cathode active material which is not suitable for the filled with sulfur atoms.

In one aspect of this application, this application provides a sulfur-containing cathode material. The cathode material comprises particles of cathode material comprising a central area, an intermediate layer and a surface layer. The middle layer is located between the core area and the surface layer. The central area comprises lithium oxide, the middle layer comprises elemental sulfur and the surface layer comprises elemental sulfur and elemental carbon. In the cathode material particle precursor, the microstructure (that is, the pores) in the interlayer is suitable for elemental sulfur filling, and the pores are small, so the cathode material can prevent sulfur from dissolving. in the electrolyte. The surface layer of the cathode material particles comprises elemental carbon and elemental sulfur. Elemental carbon can further prevent sulfur from dissolving in the electrolyte. The cathode material has a multilayer core-shell structure, and the particle structure of the cathode material does not reduce the overall packing density of the material, which contributes to the increase in the volumetric energy density of the cathode material.

In the following, the cathode material will be explained in detail by way of specific embodiments of the present application:

Since elemental sulfur is an insulator, adding sulfur to the cathode material can increase the specific capacitance of the cathode material particles, but the conductivity of the cathode material thus obtained is poor. Adding elemental carbon to the surface layer can effectively improve the overall conductivity of the cathode material. Furthermore, the elemental carbon in the surface layer can also alleviate the dissolution of elemental sulfur, that is, it can alleviate the transport effect. Unlike the conventional carbon coating that completely covers the surface of the cathode material, in the particles of the cathode material according to one embodiment of the present application, elemental carbon and elemental sulfur are dispersed in the surface layer of the particles of the cathode material, so that an uncompromised specific surface area of the cathode material particles is ensured while the beneficial effects of the traditional carbon coating are achieved. Likewise, elemental sulfur can also be distributed in a more complex backbone structure (i.e., in a backbone structure composed of lithium oxide and elemental carbon), thus better alleviating the transport effect and preventing elemental sulfur dissolves in the electrolyte.

According to an embodiment of the present application, the specific chemical composition of lithium oxide is not particularly limited and can be selected by those skilled in the art according to actual situations. For example, according to some embodiments of the present application, the lithium oxide may be composed of ternary materials. Specifically, the chemical formula of lithium oxide can be 5LiNi ^m Co ⁿ X ^(1-mn) O ² -(1-5)Li ² MO ³ , where 0 < 5 < 1, X includes at least one selected from Mn, Al, Nb, and Fe, M includes at least one selected from Mn, Al, Nb, Fe, Co, and Ni, 0 < m < 1, and 0 < n < 1. More specifically, the average valence of M in Li ² MO ³ can be 4. The average valence of X in LiNi ^m Co ⁿ X ^(1-mn) O ² can be between 3 and 4. A precursor structure of cathode material particles with pores in the precursor surface layer can be obtained with the lithium oxide particles that comply with the above chemical composition simply by controlling the synthesis procedure, where the pores in the surface layer are suitable for elemental sulfur filling.

According to a specific embodiment of the present application, the ternary material may include a nickel-cobalt-manganese (NCM) ternary material, a nickel-cobalt-aluminum (NCA) ternary material, or a lithium-rich material. The Nickel Cobalt Manganese (NCM) ternary material may be type 111 (N:C:M = 1:1:1, the following type numbers represent the atomic ratio of Nickel Cobalt Manganese in the ternary material, which will not be repeated), type 433, type 532, type 666 or type 811. The ternary nickel cobalt aluminum (NCA) material can be, for example, LiNi ^0.8 Co ^0.15 Al ^0.05 O ² . According to other embodiments of the present application, the lithium oxide can include LiNi ^{1-x and} Co ^x Mn ^and O ² , in which Mn can be replaced by any of Al, Nb and Fe, or 2, 3 or 4 of are contained. Mn, Al, Nb and Fe. When more than one element of Mn, Al, Nb and Fe is contained, the total atomic content of more than one element of Mn, Al, Nb and Fe in the ternary material meets (1-mn ) in LiNi ^m Co ⁿ X ^(1-mn) O ² .

According to one embodiment of the present application, the cathode material particles may be formed by packing lithium oxide nanoparticles. The thickness of the intermediate layer of the cathode material particles is from 0.5 gm to 20 gm, for example, 5 gm, 10 gm and 15 gm, etc., and the average size of the cathode material particles is 5 gm to 50gm, for example, 5gm, 10gm, 15gm, 20gm, 25gm, 30gm, 35gm, 40gm, 45gm and 50gm etc. The thickness of the surface layer can be from 0.2 gm to 5 gm, for example, 0.2 gm to 1 gm. It should be noted that, in this application, "surface layer" refers to an area with pores on the outer surface of the particles, i.e. an area that has a thickness in the range of 0.2 gm to 5 gm along the surface. radial direction of the particles, with the outer surface of the cathode material particles as the 0 point of thickness. The middle layer is an area with a thickness in the range of (0.5-20) gm. The area distinct from the surface layer and the intermediate layer in the cathode material particles is the core area. Taking the cross section of the cathode material particles as an example, the central part is the core area, the peripheral area that has pores filled with elemental sulfur is the middle layer, and the outermost thin layer that includes elemental sulfur and elemental carbon is the surface layer.

According to one embodiment of the present application, the cathode material particle precursor may be formed by packing lithium oxide nanoparticles. In a later step, the precursor surface layer of the cathode material particle precursor is filled with elemental sulfur, the elemental carbon is formed on the outside of the elemental sulfur, and the elemental sulfur is further dispersed by thermal melting and interpenetration treatment, to finally obtain the particles of cathode material with an intermediate layer distributed with elemental sulfur, and a superficial layer distributed with elemental sulfur and elemental carbon. The main structure in the central area is still composed of lithium oxide, so that the overall mechanical strength of the particles can be ensured and there is no collapse or rupture of bulk particles during the subsequent compaction procedure in the preparation. from the battery. The depth of sulfur penetration can be achieved by controlling the thickness of the interlayer. When lithium oxide nanoparticles with a size within the above range are packed to form a cathode material particle precursor, pores with a smaller size can be formed in the precursor surface layer in the cathode material particle precursor. Furthermore, due to the large aspect ratio of lithium oxide nanoparticles, the pores formed by packing have a small diameter and a certain depth, which prevents the electrolyte from entering the pores to dissolve the filled sulfur.

According to some embodiments of this application, the lithium oxide nanoparticles are one or more selected from rod-shaped lithium oxide and bulk lithium oxide. The lithium oxide nanoparticles are packed to form the cathode material particle precursor having pores in the precursor surface layer. The length of the lithium oxide nanoparticles can be from 0.5 gm to 2 gm, the width can be from 200 gm to 500 nm, and the aspect ratio can be from 2 to 40. The precursor surface layer of the cathode particle precursor obtained after packing lithium oxide nanoparticles having the aforementioned size have pores suitable for elemental sulfur packing having a pore size of (50-1000) nm, such as 500 nm. Elemental sulfur fills the pores to prevent the electrolyte from dissolving the elemental sulfur. The elemental sulfur loaded into the precursor surface layer can completely fill the pores of the precursor surface layer, or partially fill the pores of the precursor surface layer. That is, in addition to the elemental sulfur filled area, some pore structure can be retained in the precursor surface layer. The pore size in the precursor surface layer of the cathode material particle precursor is similar to the pore size in the cathode material particle precursor (before elemental sulfur is filled).

The present inventors find that by adjusting the morphology of lithium oxide nanoparticles and the precursor particles of cathode material formed by packing them together, for example, the size of lithium oxide nanoparticles, the gap between lithium oxide nanoparticles, lithium oxide, the particle size of the cathode material particle precursor, and others, sulfur atoms are allowed to better fill the pores of the layer surface of the precursor, to obtain a considerable filling ratio and filling stability, thus increasing the specific capacity of the cathode material. Furthermore, by adjusting the pore size in the precursor surface layer, the dissolution of sulfur atoms in the cathode material by the electrolyte can be effectively reduced, so that good cycle and battery stability are obtained. using the cathode material can achieve excellent and long service life. The useful life can be the time required for the battery to reach the end of its useful life in an open-circuit state at a certain reference temperature, that is, the life of the battery in a standby state. Particles with the above morphology can also increase the overall energy density of the cathode material without reducing the overall packing density of the material, which is beneficial for increasing the volumetric energy density of the cathode material. When the cathode material is used in a lithium ion battery, considerable battery performance can be obtained. It should be noted in particular that, in this application, the term "lithium oxide nanoparticles" or "primary particles" specifically means that the size in any dimension, such as length, diameter, and width, is at the nanometer level.

The present inventors find that, in comparison with granular or flake-shaped lithium oxide nanoparticles, after rod-shaped or bulk lithium oxide nanoparticles with the above-mentioned size are packed to form the particle precursor cathode material, the precursor surface layer of the cathode material particle precursor may have relatively regular pores suitable for accommodating elemental sulfur. The conformation of the cathode material particle precursor formed by the packing of lithium oxide nanoparticles is not particularly limited, for example, one of spherical, rhombic and ellipsoidal conformations.

According to an embodiment of the present application, the sulfur content in the cathode material is not particularly limited and can be selected by those skilled in the art according to actual situations. For example, according to some embodiments of the present application, the elemental sulfur content can be from 2% to 50% by weight, the lithium oxide content can be from 40% to 97.9% by weight, and the elemental carbon content can be be from 0.1% to 10% by weight, based on the total weight of the cathode material particles.

According to one embodiment of the present application, the sulfur content can be determined according to the pores in the precursor surface layer of the cathode material particle precursor. The present authors find that, if the elemental sulfur charge is too high, the excess sulfur that could not be filled in the pores will nucleate itself, resulting in an increase in the impedance of the material, a tendency to dissolve in the electrolyte. and strong electrochemical degradation. According to a specific embodiment of the present application, when the elemental sulfur content is within the above range, nucleation of elemental sulfur alone can be prevented. For example, the elemental sulfur content can be from 10% to 30% by weight. Elemental sulfur can be melted and then penetrate the pores. Unlike ordinary physical mixing, in case elemental sulfur melts and penetrates the pores, the presence of sulfur inside the lithium oxide particles can also be detected. Elemental sulfur can be located in a region where the thickness of the precursor surface layer of the cathode particle precursor is from 0.5 pm to 20 pm.

According to one embodiment of the present application, the elemental carbon may have a layered or bulk structure. The surface layer of the cathode material particles may also have pores made of lithium oxide, and elemental carbon and elemental sulfur may be distributed in the pores of the surface layer. The layered or bulk elemental carbon may have a thickness of (0.01 -1) pm, and the size of the layered or bulk elemental carbon (the length or width of the layered or bulk top surface) may be ( 0.5-5) pm. For example, specifically, the elemental carbon can have a layered multilayer graphite structure or be made of multilayer amorphous carbon. The thickness of the carbon layer can be 0.01 pm to 0.1 pm, and the length of the graphite layer or amorphous carbon layer can be 0.5 pm to 1 pm. Elemental carbon can be located in an area closer to the outer surface of the entire cathode particle precursor. The present authors find that when elemental carbon is located in the surface layer of the particle precursor, the conductivity of the cathode material particles can be improved without affecting the overall packing density of the final cathode material, and additional protection is provided for the cathode material. elemental sulfur, thus further preventing elemental sulfur from dissolving in the electrolyte in practical applications. For example, according to a specific embodiment of the present application, the elemental carbon can be located in an area with a thickness of less than 5 pm in the particles of the cathode material, or in an area with a thickness of 0.1 pm to 0.5 pm. As a result, a more complex multilayer structure is formed between the elemental carbon and the lithium oxide that form the particles. Elemental sulfur can fill the gaps in the multilayer structure by thermal fusion and interpenetration treatment. That is, elemental sulfur after interpenetration treatment and thermal fusion can be located in the pores (formed by packed lithium oxide nanoparticles) in the intermediate layer of the cathode material particles, or between the layers of elemental carbon in the layer surface of the cathode material particles, or in the gap between the elemental carbon layered in the surface layer and the lithium oxide nanoparticles. Therefore, a more complicated multilayer core-shell structure of cathode material particles can be formed.

According to an embodiment of the present application, the specific thickness, material, morphology and synthesis method of elemental carbon are not particularly limited, and familiar materials and methods can be selected by those skilled in the art according to actual situations for forming elemental carbon. Consequently, the electrolyte can be further blocked from entering the pores, to reduce the dissolution of elemental sulfur in the electrolyte. For example, according to a specific embodiment of the present application, elemental carbon can be formed by a method including but not limited to hydrothermal method and spray drying. Based on the total weight of the cathode material particles, the elemental carbon content may be from 0.1% to 10% by weight, for example, 3% by weight, 5% by weight or 8% by weight.

In another aspect of this application, this application provides a method of preparing a cathode material comprising particles of cathode material. The cathode material may have all the features and advantages of the cathode material described above. Specifically, with reference to Fig. 1, the method includes:

S100: Forming a cathode material particle precursor, wherein the cathode material particle precursor has a precursor central area and a precursor surface layer.

According to one embodiment of the present application, in this step, a precursor of cathode material particles is formed. As described above, the cathode material particle precursor can be formed by packing lithium oxide nanoparticles. The lithium oxide nanoparticles are rod-shaped or bulk lithium oxide nanoparticles, and the precursor surface layer of the formed cathode material particle precursor has pores suitable for elemental sulfur filling. The microstructure of the cathode material particle precursor is suitable for sulfur element filling, and the pores in the surface layer of the precursor are small, which can prevent sulfur from dissolving in the electrolyte. The particle structure of the cathode material finally obtained will not reduce the overall compaction density of the material, which facilitates the increase in volumetric energy density.

According to a specific embodiment of the present application, with reference to Fig. 2, the cathode material particle precursor can be obtained through the following steps:

S110: Form a core precursor

According to one embodiment of the present application, in this step, a solution containing metal ions, a complexing agent and a precipitating agent are mixed under stirring to obtain a precursor solution. After coprecipitation, a core precursor is obtained. The precipitating agent, the complexing agent and the solution containing metal ions are gradually added to the reactor.

As mentioned above, the cathode material particle precursor formed by packing lithium oxide nanoparticles with a certain conformation (such as a rod conformation) and size has pores that are more suitable for sulfur packing. Therefore, in this step, the morphology of the core precursor can be controlled by adjusting the stirring speed, reaction temperature, reaction pH and complexing agent concentration. Specifically, gradually added precipitating agent and other solutions can provide shear force during core precursor formation, and lithium oxide nanoparticles gradually grow and pack to form core precursor. By comprehensively controlling the stirring speed, reaction temperature, reaction pH and concentration of the complexing agent, the size and pores of the formed core precursor can be controlled, so as to control the size of the pores in the precursor surface layer. of the final cathode material particles. Specifically, the above conditions are controlled so that the lithium oxide nanoparticles obtained by lithiation have a length of (0.5-2) pm, a width of (200-500) nm, and a nanoscale particle aspect ratio of 2 -40. Lithium oxide nanoparticles sized in the above range can be packed to form a cathode material particle precursor with a precursor surface layer having pores suitable for elemental sulfur packing. According to some embodiments of the present application, controlling the above conditions, the pore size in the precursor surface layer of the cathode material particle precursor is (50-1000) nm, such as 500 nm. As a result, not only nanometer-scale particles with a specific morphology (eg, rod conformation) can be obtained, and the packed cathode material particle precursor can also have a relatively uniform pore distribution and a relatively ideal morphology.

According to one embodiment of the present application, the metal may be provided by a solution containing metal ions, and more specifically, may be provided by an inorganic salt solution containing a metal element. The metallic element includes at least one of Mn, Al, Nb, Fe, Co and Ni, and the metallic salt solution is added to the reactor with stirring. The above procedure can be carried out with heating, for example, at (30-60) °C, such as 40 °C, 45 °C, 50 °C or 55 °C. Specifically, the reactor can be placed in a water bath at (40-60) °C. The metal salt solution may include a solution for forming an NCM or NCA (without Li) material, and may be at least a nickel-containing salt solution, a cobalt-containing salt solution, and a manganese-containing salt solution, for example, a nitrate solution containing the metal ions mentioned above. The complexing agent can be an alkaline solution, eg aqueous ammonia. The concentration of aqueous ammonia can be from 5% to 15% by weight. The specific chemical composition of the metallic salt solution can be determined based on the content of metallic elements in the lithium oxide to form. The chemical composition of lithium oxide in the cathode material particle precursor has been described in detail above and will not be repeated here again.

It should be noted in particular that, in the step of forming the core precursor, the core precursor is also formed by nanoparticle packing, and the nanoparticles are subsequently lithiated to form lithium oxide nanoparticles that form the material particle precursor. cathodic. The lithiation procedure does not have a significant impact on the size of the nanoparticles. Therefore, in the step of forming the core precursor, the morphology and packing of the nanoparticles can be controlled to control the size of the lithium oxide nanoparticles in the later obtained cathode material particle precursor and the size of the pores in the precursor surface layer.

According to one embodiment of the present application, the metal ion-containing solution and the complexing agent are added to the reactor in a fixed ratio with stirring. The fixed ratio and the solution containing metal ions are determined based on the chemical composition of lithium oxide. The total amount of the solution containing metal ions in the mixed solution and the chemical composition of the metal can be determined based on the chemical composition of the lithium oxide to be synthesized. The present authors find that the stirring speed has a vital impact on the size of the later formed lithium oxide nanoparticles and on the morphology of the core precursor, further affecting the morphology of the final particles of the cathode material. When the stirring speed is (31-105) (rad/s)/min ([300-1000] rpm/min), lithium oxide nanoparticles can be obtained as described above. Specifically, the stirring speed may be (63 to 84) (rad/s)/min ([600 to 800] rpm/min).

According to one embodiment of the present application, the precipitating agent may be a reagent capable of precipitating metal ions, for example, an aqueous solution of a hydroxide, such as potassium hydroxide, sodium hydroxide, and the like. The precipitating agent can be pumped into the reactor containing the mixed solution via a variable speed drive. The pumping rate of the precipitating agent can be determined based on the pH value of the reaction system (ie, the precursor solution). The pH value is controlled at a fixed value during the reaction, or is fixed at a fixed value in the early, middle and late stages of the reaction. During the reaction process, with hydroxide coprecipitation, hydroxide ions in the system are consumed and the pH value of the system decreases. Therefore, a precipitating agent must be added to ensure the pH value of the precursor solution. When the pH value rises to a set value, the precipitating agent aggregation stops. Generally, the pH value remains unchanged throughout the reaction, that is, the pumping rate of the precipitating agent does not change, and the ratio of the added precipitating agent to the metal salt solution is approximately 2:1. Alternatively, according to other embodiments of the present application, it is also possible to control the pH to a low value in the initial stage of the reaction and then increase the pH value afterwards.

Similarly, the precipitating agent can also be added at a temperature of (30-60) °C, eg 40 °C. The amount of precipitating agent to be added is not particularly limited and can be determined by those skilled in the art based on the specific chemical composition of the lithium oxide, the total amount of the mixed solution, and the ratio of the complexing agent and metal salt solution in the mixed solution. According to a specific embodiment of the present application, the pH of the obtained precursor solution can be controlled to 10-12, eg 11, by the amount of precipitating agent added.

The precursor solution obtained after the above operation is allowed to stand at (45-60) °C for (15-30) h to cause a coprecipitation reaction. Therefore, the core precursor is easily obtained.

S120: Lithiate the nucleus precursor

According to one embodiment of the present application, in this step, the previously obtained core precursor and a lithium source are mixed and fired to lithiate the core precursor, thereby obtaining a cathode material particle precursor including a central precursor area and a precursor surface layer located outside the central precursor area.

According to an embodiment of the present application, in this step, the specific type of the lithium source is not particularly limited, and those skilled in the art can select an appropriate lithium-containing reagent according to actual needs. For example, according to a specific embodiment of the present application, an inorganic salt of lithium, such as nitrate, can be selected. The mixing ratio of the core precursor and the lithium source is not particularly limited and can be determined according to the chemical composition of the lithium oxide. The firing treatment can be carried out at a firing temperature of (600-800) °C.

According to some embodiments of the present application, the lithiation of the core precursor may be mixing the previously obtained core precursor with a lithium salt (ie, the lithium source) in water. After standing for a period of time, the precipitate is separated and dried by separation methods such as filtration, drying and evaporation. The dried precipitate is fired at the aforementioned firing temperature for a firing time that may be from 10 to 18 hours, such as 12 hours.

To further improve the quality of the obtained cathode material particle precursor, a better crystal form (such as a ternary crystal form) of lithium oxide is formed, while maintaining the pores in the previously formed core precursor. An annealing step is included after firing. Furthermore, the firing process may include rapidly raising the temperature to firing temperature, holding the temperature for a short time, and then annealing. The procedure specifically includes:

rapidly raise the temperature to roasting temperature in a relatively short period of time, such as 15 min to 1 h, holding the temperature for (0.5-2) h, and then rapidly cooling to room temperature. Rapid cooling can be placing the sample directly in a room temperature environment (where the temperature can be [0-40] °C). The quenching time for quenching can be 20 minutes to 1 hour, the annealing temperature can be 450°C to 700°C, such as 500°C, and the annealing time can be 3-8 hours, like 5 hours.

S200: Mix cathode material particle precursor with sulfur source, melt and solidify

According to one embodiment of the present application, in this step, the elemental sulfur and the cathode material particle precursor are mixed, melted, and solidified, such that the elemental sulfur fills the pores of the precursor surface layer to form a precursor of the cathode material. particles of sulfur-containing cathode material. It should be noted in particular that, in this step, elemental sulfur can also be located on the outer surface of the precursor skin layer. According to a specific embodiment of the present application, this step can be implemented by mixing the previously formed cathode material particle precursor, also known as cathode active material, with a sulfur source, followed by a melting and solidification process. Elemental sulfur can penetrate into the pores after melting. Unlike ordinary physical mixing, should elemental sulfur melt and penetrate the pores, the presence of sulfur can also be detected within the cathode material particle precursor. This cannot be achieved by simple physical mixing. Furthermore, simple physical mixing results in poor adhesion of the sulfur to the ternary material and subsequently electrical contact tends to be lost, leading to electrochemical failure. Sulfur is also easier to dissolve in the electrolyte, causing a severe transport effect.

It should be noted in particular that, although after the subsequent formation of elemental carbon, elemental sulfur will be further dispersed by thermal melting and interpenetration treatment, the elemental sulfur formed in this step by melting and solidification treatment has the above advantages, on the one hand, and is more closely bound to the particulate precursor of the cathode material, on the other hand, to prevent elemental sulfur from being evolved during the formation of elemental carbon, which will affect the yield of the finally obtained cathode material.

According to one embodiment of the present application, the cathode material particle precursor and the sulfur source can be mixed in a weight ratio of (8-12):(0.5-2). For example, the mix ratio can be 5:1,6:1,7:1, 8:1,9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15 : 1, 16:1, 17:1, 18:1, 19:1,20:1,21:1,22:1,23:1 and the like. The sulfur source may be elemental sulfur. The temperature for melting and solidification treatment can be from 120°C to 180°C, such as 130°C, 140°C, 150°C, 160°C or 170°C, and the treatment time can be 10 to 15 hours, like 11, 12, 13, or 14 hours. Specifically, the treatment can be carried out at 150 °C for 12 h. Thus, sulfur can be conveniently introduced into the pores in the outer surface, and on the outer surface, of the precursor surface layer of the previously formed cathode material particle precursor.

According to an embodiment of the present application, the melting and solidification treatment can occur under an inert atmosphere. Alternatively, the treatment can take place in a sealed and pressurized vessel under an inert atmosphere, where the vessel pressure can be (5-12) MPa. For example, according to a specific embodiment of the present application, the lithium oxide particles and the sulfur source are mixed and placed in a sealed container, and then the container is filled with an inert gas for pressurization. According to a specific embodiment of the present application, the pressure after pressurization can be 10 MPa, 8 MPa, and others.

S300: Mixing the sulfur-containing cathode material particle precursor with a carbon source and forming elemental carbon on the outer surface of the sulfur-containing cathode material particle precursor

According to an embodiment of the present application, the carbon material for forming the elemental carbon is not particularly limited and may be, for example, graphite, Ketjen black, graphene, carbon nanotubes, activated carbon, etc. The method of forming elemental carbon on the outer surface of the sulfur-containing cathode material particle precursor is not particularly limited, and may be, for example, spray-drying, and hydrothermal method. By controlling the parameters for forming elemental carbon, the elemental carbon can be located on the outer surface of the sulfur-containing cathode material particle precursor, such as in a region with a thickness less than 5 pm, for example, in a region with a thickness from 0.1 pm to 0.5 pm. For example, according to a specific embodiment of the present application, elemental carbon can be formed by spray drying. Based on the total weight of the cathode material, in this step, the content of elemental carbon formed can be from 0.1% to 10% by weight.

S400: Disperse elemental sulfur by thermal fusion and interpenetration treatment

As mentioned above, the sulfur-containing cathode particle precursor and the carbon source are mixed, and elemental carbon is formed on the outer surface of the sulfur-containing cathode particle precursor. Then, the pre-charged elemental sulfur is further dispersed by thermal melting and interpenetration treatment, so that the elemental sulfur is dispersed in the pores between the lithium oxide nanoparticles, the pores between the elemental carbon, and the pores between the carbon elemental and lithium oxide nanoparticles. Therefore, a more complicated multilayer shell-core structure of carbon dioxide can be formed. cathode lithium. As a result, elemental sulfur can be further separated from the electrolyte, making it easier to improve cycle performance and stability of the battery using the cathode material. The temperature for heat fusion and interpenetration treatment can be 100°C to 200°C, and the treatment time is 2 to 10 hours. For example, the treatment can be implemented by heat treatment at a temperature of 100°C to 160°C for 3-6 hours.

In another aspect of this application, this application provides a cathode material. According to one embodiment of the present application, the cathode material is as described above, or is prepared by the method described above. Therefore, the cathode material has all the features and advantages of the cathode material obtained by the method mentioned above, and will not be repeated here again.

In another aspect of this application, this application provides a lithium ion battery. The lithium ion battery includes the cathode material as described above. Therefore, the lithium ion battery has all the features and advantages of the cathode material as described above, and will not be repeated here again. In general, the lithium ion battery has a higher energy density and a better life cycle.

In another aspect of this application, this application provides a means. According to one embodiment of the present application, the means includes a lithium ion battery as described above. For example, the means may include a plurality of battery packs comprised of the aforementioned lithium ion batteries. Therefore, the medium has all the features and advantages of the lithium ion battery described above, and they will not be repeated here again.

The solutions of the present application are described below with reference to the embodiments. A person skilled in the art can understand that the following embodiments are only used to describe the present application and should not be construed as limiting the scope of the present application. Specific technologies or conditions not indicated in the embodiments are performed according to the technologies or conditions described in the documents in this field or according to a product specification.

Example 1: Production of cathode material

(1) 50 mmol of nickel nitrate and 50 mmol of cobalt nitrate were dissolved in 100 g of water, pumped into a stirred hydrothermal reactor, and stirred at 63 (rad/s)/min (600 rpm/min) . 5 g of aqueous ammonia (having a concentration of 10% by weight) was added at a constant rate, the aqueous ammonia being pumped at the same rate as the saline solution. Sodium hydroxide was added to adjust the pH to 11. Coprecipitation was carried out at 30 °C for 24 hours and a core precursor was obtained by filtration.

(2) The core precursor was mixed with lithium nitrate in water. The precipitate was filtered off, dried, then baked at 700 °C for 1 h, removed, allowed to cool to room temperature in 30 min, and then annealed at 500 °C for 5 h. A ternary cathode material particle precursor was obtained.

(3) The ternary cathode material particle precursor was mixed with elemental sulfur in a weight ratio of 10:1, then heat treated in a muffle furnace, reacted at 150 °C for 12 hours, extracted, dried and pulverized to obtain a sulfur-containing cathode material particle precursor.

(4) The sulfur-containing cathode material particle precursor and graphene were spray-dried in a weight ratio of 100:5, and then added to a hydrothermal reactor and heat-treated at 150 °C for 4 hours to obtain particles of cathode material.

Example 2: Production of cathode material

The steps were the same as in Example 1, except that the ternary cathode material particle precursor and elemental sulfur were mixed in a 10:0.5 weight ratio and then reacted in a hydrothermal reactor at a temperature of 150 °C for 12 hours.

Example 3: Production of cathode material

The steps were the same as in Example 2, except that in step (3), the ternary cathode material particle precursor and elemental sulfur were mixed in a weight ratio of 8:1. Step (4) was as follows.

(4) The sulfur-containing cathode material particle precursor and graphene were spray-dried in a weight ratio of 100:8, and then added to a hydrothermal reactor and heat-treated at 150 °C for 4 hours to obtain a cathode material.

Example 4: Production of cathode material

The steps were the same as in Example 2, except that steps (3) and (4) were as follows.

(3) The ternary cathode material particle precursor and elemental sulfur were mixed in a 14:1 weight ratio, fed to a hydrothermal reactor, pressurized by introducing an inert gas, sealed, and they reacted for 12 hours at 150 °C under a pressure of 10 MPa. The obtained material was dried and pulverized to obtain a sulfur-containing cathode material particle precursor.

(4) The sulfur-containing cathode material particle precursor and graphene were spray-dried in a weight ratio of 100:8, and then added to a hydrothermal reactor and heat-treated at 150 °C for 4 hours to obtain a cathode material.

Comparative Example 1

(1) 50 mmol of nickel nitrate and 50 mmol of cobalt nitrate were dissolved in 100 g of water, and then 5 g of aqueous ammonia (with a concentration of 10% by weight) were added. Sodium hydroxide was added to adjust the pH to 11. Coprecipitation was carried out at 30 °C for 24 hours and a core precursor was obtained by filtration.

(2) The core precursor and lithium nitrate were mixed in water, removed, dried and fired at 700 °C for 5 hours to obtain a ternary cathode material particle precursor.

(3) The ternary cathode material particle precursor, elemental sulfur and acetylene black were mixed directly in a weight ratio of 100:10:5.

Comparative example 2

(1) 50 mmol of nickel nitrate and 50 mmol of cobalt nitrate were dissolved in 100 g of water, and then 5 g of aqueous ammonia (with a concentration of 10% by weight) were added. Sodium hydroxide was added to adjust the pH to 11. Coprecipitation was carried out at 30 °C for 24 hours and a core precursor was obtained by filtration.

(2) The core precursor was mixed with lithium nitrate in water, removed, dried, and then fired at 700°C for 1 hour. The obtained material was removed while at 700 °C, quickly cooled to room temperature, and then annealed at 500 °C for 5 h. A ternary cathode material particle precursor was obtained.

(3) The ternary cathode material particle precursor, elemental sulfur and acetylene black were mixed directly in a weight ratio of 100:10:5.

performance test

1. Characterization of morphology

The morphologies of the samples obtained in the previous examples and the intermediates during the preparation procedure were observed under a scanning electron microscope (SEM).

Referring to Fig.3, the lithiated cathode material particles obtained in Examples 1 to 4 are spherical particles of about (5-10) pm, and the pore diameter in the intermediate layer of the particles is about 500 nm to 1 pm.

The active materials formed with elemental carbon obtained in Examples 1 to 4 are shown in Fig. 4. Elemental carbon is formed in the pores of the surface layer of the particles and is partially distributed on the surface of the carbon oxide particles. lithium. The morphology after interpenetration treatment and thermal fusion is shown in Fig. 5. The results of the test are shown in Table 1.

2. Sulfur content test

Samples obtained from the above examples and comparative examples were analyzed for sulfur content. Specific test steps and methods: The overall sulfur content in the material was tested by a carbon-sulfur analyzer. The test results are shown in Table 1.

Table 1. Results of the tests of the samples

It can be seen from the test results that the obtainable materials in the examples and comparative examples all have considerable sulfur content. Furthermore, since the elemental sulfur and the ternary cathode material are mixed directly without heat treatment in the two comparative examples, a higher sulfur content test result is shown when the sulfur content is tested directly.

3. Volumetric energy density test

Specific test method: 5 g of the cathodic materials obtained in the above examples and comparative examples, respectively, were taken, mixed with a cathodic conducting agent and a cathodic binder, fed into a mold with a diameter of 2 cm, and pressed. with a pressure of 10 MPa to obtain a powder. The volumetric energy density of the cathodic active material was calculated as follows.

The highest height to which the powder can be pressed under the above pressure is h, and the compaction density of the powder is p = 5 / ni2h.

The energy density is calculated using the following formula:

Energy density = specific capacity * average charge voltage * compaction density of the powder.

The test results are shown in Table 2:

Table 2. Results of the energy density tests of the samples

It can be seen from the test results that although the samples obtained in Comparative Example 1 and Comparative Example 2 have a higher sulfur content in the sulfur content test, their energy density is significantly lower than that of the samples obtained in the examples. This is because the sample is a cathodic material during the sulfur content test. Therefore, in the samples of the comparative examples formed by direct mixing, part of the elemental sulfur is adsorbed on the surface of the ternary material by physical adsorption. However, after the cathode material is subjected to the above battery preparation procedures (such as coating, drying, and sootblowing, etc.), some of the physically adsorbed elemental sulfur will be lost, but heat-treated samples of the Example 1 to Example 4 will not suffer the loss as in the comparative examples. Furthermore, after the cathode sample is in contact with the electrolyte, the cathode materials prepared in Comparative Example 1 and Comparative Example 2 do not have the particle morphology of Example 1 to Example 4, so dissolution of the elemental sulfur charged in them after contact with the electrolyte can not be relieved. In Comparative Example 1, the core precursor is synthesized without stirring, so the morphology of the core precursor cannot be controlled well; and only a simple one-step heat treatment is performed during core precursor lithiation, so core precursor morphology cannot be well preserved. Therefore, the finally obtained cathode material particles have neither an intermediate layer nor a surface layer. In Comparative Example 2, although rapid quenching and annealing are performed in the lithiation process to maintain a certain morphology (with pore structures in an outer area having a thickness of 1 to 5 microns), elemental sulfur only adheres to the surface, so the dissolution of elemental sulfur cannot be avoided. Also, the sulfur source is not heat treated, but mixed directly. Therefore, the adhesion between sulfur and ternary material is poor and electrical contact tends to be lost subsequently, resulting in electrochemical failure and unsatisfactory energy density. Furthermore, the morphology of the particles from Example 1 to Example 4 can also maintain the compaction density of the material as a whole after the compaction procedure, which is more conducive to obtaining a considerable energy density.

In the description of the present specification, the description of the terms of reference "an embodiment", "another embodiment" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment. least one embodiment of the present application. In the present specification, the illustrative expression of the above terms does not necessarily refer to the same embodiment or example. Likewise, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments. Moreover, in the case that they do not contradict each other, the person skilled in the art will be able to combine or group different embodiments or examples that are described in the present specification and the features of the different embodiments or examples.

Implementations of the present application are described in detail above. However, the present application is not limited to the specific details of the above implementations, various simple variants on the technical solutions of the present application can be made within the scope of a technical concept of the present application, and all simple variants fall within the scope of protection of this application.

It should further be noted that the specific technical features described in the above specific embodiments may be combined in any suitable manner without contradiction. Furthermore, the various implementations of the present application can be combined without departing from the idea of the present application, and such combinations will also be within the scope of the present application.

Claims (14)

1. A cathode material, comprising cathode material particles, wherein the cathode material particles comprise a core area, an intermediate layer and a surface layer, wherein the intermediate layer is located between the core area and the surface layer; and the central area comprises lithium oxide, the middle layer comprises elemental sulfur, and the surface layer comprises elemental sulfur and elemental carbon, wherein: lithium oxide comprises 5LiNi ^m Co ⁿ X ^(imn) O ² -(1-5)Li ² MO ³ , 0 < 5 < 1, X is at least one selected from Mn, Al, Nb and Fe, M is at least one selected from Mn, Al, Nb, Fe, Co and Ni, 0 < m < 1 and 0 < n < 1. 2. The cathode material according to claim 1, wherein the particles of the cathode material have an average particle size of (5-50) gm, the middle layer has a thickness of (0.5-20) gm, and the surface layer has a thickness of (0.2-5) gm. The cathode material according to claim 1 or 2, wherein the cathode material particles have at least a spherical, rhombic and ellipsoidal shape. 4. The cathode material according to any one of claims 1 to 3, wherein, based on the total weight of the particles of the cathode material, the elemental sulfur content is (2-50)% by weight, the oxide content lithium is (40-97.9)% by weight and elemental carbon content is (0.1-10)% by weight. The cathode material according to any one of claims 1 to 4, wherein the intermediate layer further comprises lithium oxide, a pore structure is formed by packing the lithium oxide and elemental sulfur fills the pore structures. A method of preparing a cathode material according to any one of claims 1 to 5, the cathode material comprising particles of cathode material, and the method comprising: mixing a solution containing metal ions, a complexing agent and a precipitating agent with stirring, coprecipitating to obtain a nucleation precursor, and mixing the nucleation precursor with a lithium source and firing to obtain a cathode material particle precursor formed by the lithium oxide packing and comprising a precursor core area and a precursor surface layer located outside the precursor core area, wherein the metal comprises at least one of Mn, Al, Nb, Fe, Co and Ni, and the lithium oxide comprises 5LiNi ^m Co ⁿ X ^(1-mn )O ² (1 -5)Li ² MO ³ , 0 <5 <1, X comprises at least one of Mn, Al, Nb and Fe, M comprises at least one of Mn, Al, Nb, Fe, Co and Ni, 0 < m < 1 and 0 < n <1; mixing the cathode material particle precursor with a sulfur source, melting and solidifying, to fill the precursor surface layer with the elemental sulfur to obtain a sulfur-containing cathode material particle precursor; mixing the sulfur-containing cathode material particle precursor with a carbon source and forming elemental carbon on the outer surface of the sulfur-containing cathode material particle precursor; and dispersing elemental sulfur by thermal melting and interpenetration treatment to obtain cathode material particles with a surface layer comprising elemental sulfur and elemental carbon. The method according to claim 6, wherein the cathode material particle precursor is formed by packing lithium oxide nanoparticles, and the length of the lithium oxide nanoparticles is (0.5-2) gm, the width of lithium oxide nanoparticles is (200-500) nm, and the aspect ratio of lithium oxide nanoparticles is 2-40. The method according to claim 7, wherein the precursor skin layer has pores, and elemental sulfur fills the pores; and the pore size is (50-1000) nm. 9. The method according to any one of claims 6 to 8, wherein the core precursor is obtained at (30-60) °C, the pH of the solution in the coprecipitation treatment is 10-12, the stirring speed is (31-105) (rad/s)/min ([300-1000]rpm/min), and the weight percent content of the complexing agent is (5-15) wt%. The method according to any one of claims 6 to 9, wherein the metal ion-containing solution comprises at least one of Mn ions, Al ions, Nb ions, Fe ions, Co ions and Ni ions; the complexing agent comprises aqueous ammonia; and the precipitating agent comprises potassium hydroxide and sodium hydroxide. The method according to any one of claims 6 to 10, wherein the cathode material particle precursor and the sulfur source are mixed in a weight ratio of (8-12):(0.5-2); and the temperature for the melting and solidification treatment is (120-180) °C, and the treatment time is (10-15) h. The method according to any one of claims 6 to 11, wherein the temperature for the interpenetration and thermal fusion treatment is 100°C to 200°C, and the treatment time is 2h to 10h. The method according to any one of claims 6 to 12, wherein the sulfur-containing cathode material particle precursor and the carbon source are mixed in a weight ratio of 100:(10-0.1) and dried by spray; and the thermal fusion and interpenetration treatment is a thermal treatment at a temperature of (100-200) °C and a time of (1-10) h. A lithium ion battery comprising a cathode material according to any one of claims 1 to 5, or a cathode material prepared by the method according to any one of claims 6 to 13.